I trusted the same person to cut my hair for about 8 years while living in New Orleans. After Katrina I became a bit of a vagabond and was pretty apprehensive about paying so much to let someone chop away, so I started doing it myself. I keep it pretty short and kind of messy, so I followed my aunt's advice to buy shearing scissors (around $12). They seem to make mistakes less apparent and help to blend the hard lines that straight scissors leave. If there's considerable length that needs cutting, I use standard scissors for the perimeter, then blend with shearing scissors. If it's just a touch up that's needed, shearing scissors alone will usually do the trick.

To cut the back, I put a mirror on my art easel and adjust it to face the bathroom mirror at a slight angle. Whatever it takes to have one mirror face the other, so as to view the back as you cut, will work. Some medicine cabinet mirrors work well because you can adjust the angle as needed. I tried using a handheld mirror for a while, but it's very difficult to hold a mirror, comb, and scissors while trying to actually cut. It's enough of a challenge overcoming the illusion created by the two mirrors.

Using a comb to make sure you have ample space between your scalp and the cut line the way you've seen professionals do will help to avoid creating gaps, though it's not as easy as it looks.

Obviously, cutting the front should be less daunting, but tread lightly at first. Cutting less than you think you should and going back to touch up is better than getting over-zealous and ending up looking like Mr. Spock or that second-grade picture (yeah, you know the one).

You can always pay to go to a good stylist occasionally. Ask their opinion of the overall cut and pick up some pointers as they work.

It takes time and patience, but definitely pays off, in dollars and convenience, once you get the hang of it. Good luck.

I misunderstood or didn't actually read... one of the two.
I realize from re-reading that you're dealing with a much shorter cut.
My advice won't help much. Please disregard.

$8 is the price of the tip for a *trim* for most women... let's not even talk about the price of the trim or a cut... don't want to think about color or highlights or other treatments...

I have to update this post as the last time my sweetie trimmed the back of my hair for me he did a great job. When I went in a week or two later to have the doo touched up I told the beautician that my hubby had cut the back and she said, "He's hired." :)